Compositor : export output node when we want ?
Yes, if it was just a still render image, you can save each passes as a single image:



Just select the render pass, then go to Image > Save Image as

But if you want to render an entire animation without having to "Use Nodes" or even if you want to save the still render image passes as a single image file, you can save the render as an OpenEXR Multilayer file, but consider that the image file size could increase a lot.